The latest Firefox has the obligatory speed boost -- Mozilla claims it's "up to six times faster than the previous release" -- courtesy of an improved JavaScript engine and hardware acceleration. It also has new security features like the Content Security Policy for preventing cross-scripting attacks and is the first to include the Do Not Track feature, which allows users to opt out of third-party Web tracking.

Users will likely notice the redesigned interface immediately, which has taken a minimalist bent reminiscent of Google's Chrome. The new interface goes beyond the cosmetic: The App Tabs feature gives users easy access to frequently visited sites, and the new Panorama feature lets users bundle tabs into groups with a drag-and-drop interface. Also, boosted synchronization capabilities mean that users can sync their bookmarks across different computers and with Android-based mobile phones for the first time.

For developers, Firefox 4's JavaScript engine incorporates the new JägerMonkey JIT compiler and enhances support for such tools as CSS and Canvas. On the HTML5 side, Firefox 4 supports WebM high-definition video, offline data storage, touch interfaces, and the Mozilla Audio API.